ASSERT "vsyscall incorrect assumption" on AMD 32-bit

[derekbruening]

This is now showing up on the GA CI VM's since they now use AMD hardware.

Xref DynamoRIO/dynamorio#6417 where 32-bit AMD machines added to GA CI caused a lot of test failures. This looks similar.

https://github.com/DynamoRIO/drmemory/actions/runs/7515048417/job/20458582246?pr=2490

15:   ~~Dr.M~~ ASSERT FAILURE (thread 43342):
15:   /home/runner/work/drmemory/drmemory/drsyscall/drsyscall_linux.c:239:
15:   !is_using_sysint() (vsyscall incorrect assumption)